The present invention relates to a viscous fluid clutch adapted to drive an accessory device, such as a cooling fan, for an internal combustion engine.
Japanese Utility Model Application First Publication No. 4-105641 discloses a viscous clutch adapted to drive an accessory device, such as a cooling fan, for an internal combustion engine. This known viscous fluid clutch includes relatively rotatable first and second drive members having a fluid shear space therebetween and which are cooperable with a fluid medium in the shear space to provide a shear-type fluid drive therebetween, and a fluid reservoir for storing the fluid medium. With viscous fluid clutch, in response to a rapid increase in rotational speed of the second drive member, the first drive member follows this change in rotational speed. Thus, the overshoot phenomena of the first drive member will take place when subsequently the rotational speed of the second member decreases.
An object of the present invention is to improve this known viscous clutch such that the overshoot pheneomena is avoided or at least suppressed.